Consider that Adata does not make harddrives; WD does.
You'll know you have a WD drive in your WD external. You have no idea what will be in the Adata and its likely to be the cheapest drive they could source at the time; kind of like the way all bids work.
AS for the advice, lonewolf is right. external drives tend to fail more for a variety of reasons. The very enclosure tends to trap heat and the hotter a drive runs the sooner it will fail. External drives get moved, carried, and eventually dropped. Sure a rubberized housing helps but your still applying an impact to the mechanical drive.
IMO external drives are for moving copies of data and should never be used to store the only copy. Just look thru our fourms and see how many users are trying to recover data from their externals... Its a bitter pill to swallow.
If you really need an external drive, go ahead and get one, read reviews to try and get a quality one, always remember to eject the drive and not just disconnect it. Never move while its ON. And never trust it (or any drive) to hold your only copy of important data.